1. Field of the Invention
The present invention relates to a plasma processing apparatus which processes a substrate by generating plasma in a process vessel.
2. Description of the Related Art
Processing using plasma is widely used in substrate processing such as etching and deposition in manufacturing processes of, for example, semiconductor devices, liquid crystal display devices, and the like.
The plasma processing is usually performed in a plasma processing apparatus. This plasma processing apparatus includes upper and lower electrodes facing each other in a process vessel, and radio-frequency power is supplied to the lower electrode on which, for example, a substrate is placed, to generate plasma between the lower electrode and the upper electrode, thereby processing the substrate.
In the above-described plasma processing, radio-frequency current flows in the plasma from the lower electrode to the upper electrode when the radio-frequency power is supplied. This radio-frequency current contributes to the generation of the plasma, and the state of the plasma such as plasma density, a self-bias (Vdc), and the like is closely correlated with the radio-frequency current. Therefore, the radio-frequency current is an important factor in evaluating the processing state of the substrate. For example, in a case where an amount of the radio-frequency current flowing from the lower electrode to the upper electrode is measured, it is conceivable to attach a current sensor between the lower electrode and a matching circuit, that is, on an output side of the matching circuit. For reference, there has already been disclosed an art in which, in order to detect a degree of peeling (a consumption degree) of the lower electrode ascribable to sputtering, a circuit for measuring current is provided between the lower electrode and a matching circuit, thereby detecting the consumption degree based on the measured value (see Japanese Patent Application Laid-open No. 2002-43402. and U.S. Pat. No. 6,879,233).